(1) Field of the Invention
The present invention relates to a resin composition. More particularly, the present invention relates to a nylon-4,6 resin composition having excellent moldability and excellent heat stability.
(2) Description of the Related Art
Nylon-4,6 resins produced from a tetramethylenediamine or its functional derivative and adipic acid or its functional derivative are well known, and are believed to have a high utility value as an engineering plastic because they have superior mechanical strength (e.g., tensile strength, bending strength, impact strength), heat resistance, and sliding characteristics. Nylon-4,6 resins, however, have a serious drawback of poor moldability, making their utilization extremely difficult.
Generally the moldability of polymers, particularly plastics, is very important in the evaluation of plastics per se. Even if a plastic inherently possesses excellent properties, if it has a poor moldability, it is difficult to economically produce a molding therefrom, and moreover, it is impossible for the molding to satisfactorily retain the excellent properties of the plastic raw material.
The nylon-4,6 resins have a melting point of about 290.degree. C. but decompose at about 320.degree. C. or above, and accordingly, the temperature range in which the resins are moldable is very narrow.
Moreover, the melt viscosity of nylon-4,6 resins which are used as an ordinary molding material not only is extremely temperature-dependent but also is substantially reduced due to thermal decomposition during residence. Therefore, the flowability of these resins in the molten state can vary greatly, due to a minor change of molding temperature and residence time in the molten state, etc., making it very difficult to produce a stable mold thereof.
This instability of a melt during molding causes drooling during the molding, and the molding obtained has defects, such as short shot, sink, flow mark, flash, etc., and as a result, the molding has a poor appearance and remarkably reduced mechanical strengths.
WO No. 86/03214 discloses an improvement of the stability of nylon-4,6 during melt-molding by the addition thereto of at least one compound selected from the groups of aminosilanes, epoxysilanes and vinylsilanes. However, the resulting composition does not have sufficient heat stability during molding, and a further improvement is required.